Uninsulated basements are recognized as a significant source of heat loss in homes. Basement walls typically extend above the grade of soil which is backfilled along the exterior of the basement walls. Below grade, soil has some degree of insulative value, however depending upon the severity of climate, soil may freeze many feet below grade. Heat from the interior of the basement may be conducted through the walls and lost to the relatively cooler soil. Where the water content of the soil is high as in the eastern portions of North America, the insulative value of the soil declines and basement heat loss through conduction may become substantial. In addition, where exterior moisture in the soil penetrates the basement walls a number of effects may ensue. Moisture may freeze in the wall and expand, thereby damaging the walls. When such moisture penetrates to the warm interior surface of the wall it evaporates, and the energy required for this evaporation comes from the heat content of the basement air and results in a temperature drop. Thus it is important to protect the basement from loss of heat through both conduction and evaporation. Water vapour inside a basement may also penetrate a basement wall, moving from the interior to the exterior of the wall until it freezes, at which time it expands causing damage similar to that when exterior moisture in the soil penetrates the basement walls.
Above grade, the joists of a home sit on the top of the basement walls, creating an air space which must be insulated against loss of heat through conduction and infiltration of air from the outside. It is therefore necessary to insulate a basement wall over the surface area extending from the joist spacing to at least the limit at which the surrounding soil may freeze. To this end building codes for new homes have set limits for the thermal resistance (R value) of basement walls and the permeability of barriers to be applied to prevent the movement of interior water vapour into walls.
One method of construction which is used most widely in the erection of new homes in Canada, calls for basements constructed of cast in place concrete. Below grade, the exterior of the concrete wall is coated to make it substantially impermeable to moisture. The interior surface of the wall is insulated against the conduction of heat and a vapour barrier is used to cover the surface of the insulation which is facing the warm air of the basement. Typically in new homes batts of fibreglass insulation are the chosen insulative material. Present construction methods typically consist of affixing a breather type sheating paper (such as tar paper) to the basement inner wall extending from the sill plate on top of the basement wall down to the chosen limit of insulation. Wood strapping is then affixed over the sheating paper to provide a grid of compartments of sufficient depth to accommodate standard sizes of fibreglass batts which are supported in the compartments by a frictional fit. The strapping and batts are then covered with a vapour barrier, such as 6 mm thick polyethylene. Fibreglass batts are then stuffed into the joist spacing and a separate application of a vapour barrier is placed over the insulation.
A number of disadvantages are associated with the installation of fibreglass batts according to present construction methods:
(a) Cast in place concrete basement walls have surface undulations. When wood strapping is installed abutting the wall there are intermittent gaps of approximately three inches (3") between the strapping and the wall. Shims are used to support the strapping proximate these gaps. It is therefore difficult to maintain a close fit between the wall and the strapping, and between the batts and the wall. Spaces are created between the wall and the vapour barrier where moist air can circulate. The application of sheating paper next to the basement inner wall cannot entirely protect the wood from circulating moisture. The wood strapping is therefore subject to mildew and fungus. It has been known to eliminate the use of wood as a material for supporting insulation in applications above a basement. For example, in the case of metal buildings where a combination of insulation and reinforced nylon vapour barrier is glued to the interior surface of a roof or where such insulation is glued to the interior surface of walls.
(b) Typically construction code requirements stipulate use of insulation adjacent to the basement wall of a thermal resistance rated at R8 and in the joist spacing at R12. The average thermal resistance of wood strapping is R1.5--therefore when the batts of insulation are placed in a wood strapping framework by frictional fit, the strapping provides a thermally conducting bridge of lower resistance than the batts thereby lowering the thermal resistance of the insulative barrier composed of R8 fibreglass batts and R1.5 strapping to approximately R4 in place.
(c) The joist spacing is insulated by an application of batts separately from the wall. In practice the 6 mm polyethylene vapour barrier is not continuous because it is applied over the joist spacing and wall separately. Air may circulate across the barrier at the seam of adjoining sections of 6 mm polyethylene or where the vapour barrier is punctured when it is stapled in place.
(d) The installation of fibreglass batts is labour intensive and therefore an added cost in as much as six identifiable labour steps are involved: (i) apply sheeting paper moisture barrier to wall, (ii) install wood strapping frame comprising carpentry, (iii) cut to size and install fibreglass batts between strapping, (iv) apply vapour barrier over installed insulation on wall, (v) cut to size and install fibreglass batts in joist spacing, and (vi) apply vapour barrier over installed insulation in joist spacing.
(e) Usually builders only meet minimum building code requirements and insulate only the partial height of the wall extending from the top of the wall. Where a homeowner wishes to finish a basement wall to the full wall height, that is, extend the insulation to the floor, the existing application of insulation cannot be removed to accommodate a full wall height structure without damaging it since it is not mechanically fastened to the basement wall.
It is therefore an object of this invention to provide an improved system for insulating the interior surface of basement walls.
It is a further object of this invention to provide an improved method of installing insulation in basements.
Further and other objects of this invention will be realized by those skilled in the art from the following summary of the invention and detailed description of preferred embodiments thereof.